1. Field of the Invention
The present invention relates to a dishwasher for cleaning dishes or the like efficiently by jetting cleaning water from jetting openings thereof.
2. Description of the Related Arts
A conventional method for operating a dishwasher is described below with reference to FIG. 22. Upper and lower dish containers 102 and 103 for accommodating dishes are disposed vertically in a plurality of stages in a tank 101. Upon start of drive with detergent put into the tank 101, a predetermined amount of cleaning water is supplied to the tank 101. Then, cleaning water, including detergent, pressurized by the pump 104 is jetted from the nozzles 105 and 106. Then, cleaning water including leftover or the like washed away from dishes is discharged from the dishwasher. Thereafter, cleaning water is jetted vertically or obliquely upward from the jetting opening of each of the nozzles 105 and 106. As a result, the nozzles 105 and 106 are rotated substantially horizontally by a reaction to the jetting force. Accordingly, most of the cleaning water inclines in the direction opposite to the rotational direction of the nozzles 105 and 106, thus colliding with the dishes. The dishes are washed by the colliding force of the cleaning water, the detergent, and heat.
After the cleaning process which is performed for a predetermined period of time terminates, cleaning water including leftover or the like washed away from the dishes is discharged from the dishwasher. Then, cleaning water is supplied to the tank 101 again and jetted to the dishes from the nozzles 105 and 106 to wash the dishes again and then, the cleaning water is discharged from the dishwasher. These operations are performed four times before cleaning process terminates. The dishwasher further comprises a heater 107, a pump 104, and a control device 107 for controlling the operation of the heater 107 and the like.
In the above-described dishwasher, the pressure of the cleaning water jetted from the first nozzle 106 is greater than that of the second nozzle 105. Therefore, the lower dish container 103 is used to clean dishes on which rice, oil, egg or the like have been left. Since the first nozzle 106 comprises a single arm which rotates substantially horizontally, the rotation locus of the jetting opening of the first nozzle 106, namely, the jetting locus of cleaning water jetted from the first nozzle 106 is constant. That is, the cleaning water is not jetted to every portion of each dish at a uniform intensity, but is repeatedly jetted to particular portions thereof. Therefore, the dishwasher has a low cleaning efficiency. That is, cleaning water cannot be jetted to the entire space (region to be cleaned) including the dish containers 102 and 103 and the dishes. Therefore, it is necessary for the jetting opening to allow the generation of a great pressure and flow rate. Consequently, a large motive power is supplied to the first nozzle 106. Energy calculated from the discharge pressure of cleaning water and flow rate thereof is hereinafter referred to as motive power of cleaning water. Consequently, the pump 104 is required to have a great pressurizing capability and thus great noises are generated in operation and in addition, cleaning water drips to the tank 101 in a large quantity, thus generating great noises.
In addition, since the performance for cleaning the dishes on the lower dish container 103 is not favorable, in the final stage of washing process, it is likely that leftover washed away from dishes attaches to the back surfaces of the dishes. In particular, leftover washed away from dishes in the upper dish container 102 attaches to the back surfaces of the dishes placed in the lower dish container 103.
In the conventional dish container, dishes, in particular, a plate can be placed in the dish container with the upper surface thereof turned over. But the number of cleaning arm nozzles is two and disposed vertically and in addition, cleaning water is jetted from each arm in a fixed locus. Therefore, when dishes are jetted in a direction opposite to the direction in which cleaning water is jetted, the cleaning water has a very low cleaning performance and thus it is inconvenient to use the dishwasher.
In the dishwasher in which the first nozzle 106 and the second nozzle 105 are vertically disposed, the rotational region thereof is vertically great and thus a dish-accommodating region has to be small. Thus, a large number of dishes having a great diameter cannot be placed in the dish container. Thus, it is inconvenient to use the dishwasher.
Due to the improvement of cleaning efficiency, it is possible to greatly reduce the jetting pressure generated at the jet opening and the flow rate of cleaning water. But due to the reduction in circulation amount of cleaning water of the pump 104, leftover cannot be reliably collected by the filter 112 at a predetermined position thereof and is thus scattered on the bottom surface of the tank 101. Thus, the leftover is scattered on the bottom surface of the tank 101 and unsanitary.
Further, since the first nozzle 106 rotate in an upper plane and the second nozzle 105 rotate in a lower plane, the distance between the jetting opening of the second nozzle 105 and the dishes in the dish container 103 is different from the distance between the jetting opening of the first nozzle 106 and the dishes in the dish container 103. Thus, it is impossible to jet cleaning water to the dishes in an appropriate distance in dependence on the configuration of the jetting openings. In order to overcome this disadvantage, it is necessary to increase the motive power of cleaning water.
In a dishwasher according to U.S. Pat. No. 3,468,486, a cleaning nozzle comprising a first arm nozzle and a second arm nozzle is used to improve its cleaning performance. In the dishwasher, the rotation axis of the second arm nozzle is eccentric from that of the first arm nozzle. When the operation of the dishwasher is stopped or cleaning process terminates, the cleaning nozzle inclines to one side, namely, to the first arm nozzle, thus becoming stationary. Because the distance between the first arm nozzle and a heater disposed below the first arm nozzle is short, the temperature of the first arm nozzle becomes high during drying process. Therefore, if the first arm nozzle is made of an inexpensive and low-grade resin, it is thermally deformed. It is conceivable to compose the first arm nozzle of metal, but the first arm nozzle has a high temperature when drying process has terminated, which may cause an operator to be got burnt in the hand. In addition, in composing the cleaning nozzle of a metal plate, it is difficult to configure the cleaning nozzle which has a favorable cleaning performance and does not make a large noise.
Even though the cleaning nozzle is balanced between the left side thereof and the right side in weight, the cleaning nozzle inclines to either the first arm nozzle side or the second arm nozzle if the weight of cleaning water staying in the first arm nozzle is not balanced with that of cleaning water staying in the second arm nozzle. At this time, cleaning water remains inside the first arm nozzle or the second arm nozzle and thus leftover contained in the cleaning water is accumulated therein, thus giving a bad smell.
In the construction of the dishwasher according to U.S. Pat. No. 3,468,486, it cannot be said that cleaning water jetted into the tank cleans dishes with a very high efficiency. That is, cleaning water is jetted from a first jetting opening of the first arm nozzle to dishes in a narrow annular space while it is rotating on its axis. A second jetting opening of the second arm nozzle rotates on the rotation axis thereof, with the second jetting opening rotating on the rotation axis of the first arm nozzle in accordance with the rotation of the first arm nozzle, thus jetting cleaning water toward the dishes. In combination of the first and second jet openings, cleaning water can be jetted uniformly and in a wide angle toward the dishes. But the cleaning range covered by the second jetting opening is very large. Therefore, the energy of cleaning water per area decreases by geometrical progression from the center of the cleaning tank toward the periphery thereof. In order to solve this problem, it is necessary to use a pump having a high motive power so as to jet cleaning water having a high energy from the first jetting opening to the outside region of the rotation locus of the second jetting opening. As a result, the magnitude of a downward moment generated by reaction, to jetting force, generated at the first jetting opening is much different from the magnitude of a downward moment generated by reaction, jetting force, generated at the rotation axis of the second arm nozzle. Consequently, an unbalance is generated vertically on the rotary plane of the first arm nozzle with respect to the rotation axis thereof 01 and thus the first arm nozzle is incapable of rotating horizontally. Accordingly, an unfavorable rotation occurs and as a result, a large quantity of water not contributing to dish washing leaks from a sealing portion, which reduces the cleaning performance of the dishwasher.
In order to solve this problem, it is necessary for the second arm nozzle to rotate on the rotation axis 01 of the first arm nozzle in a radius more than is required. But there are limitations to enlarging the distance between the rotation axis of the second arm nozzle and the position of the first jetting opening. As such, it is difficult to form the construction which allows the second arm nozzle to rotate horizontally on the rotation axis 01 of the first arm nozzle in a great radius.
Further, pipe resistance to pressurized cleaning water between the first arm nozzle and the second jetting opening is greater than pipe resistance to pressurized cleaning water on the first jetting opening side, and thus the discharge pressure of cleaning water jetted from the second jetting opening and the quantity of the cleaning water jetted therefrom are lower than those of cleaning water jetted from the first jetting opening by 10% to 20%. That is, the dishwasher has a problem that the cleaning water jetted from the second jetting opening has a small energy density and that the effective motive power of the cleaning water jetted from the second jetting opening is much lower than that of the cleaning water jetted from the first jetting opening.
In addition, only dishes in the lower dish container can be cleaned at a high efficiency. Therefore, dishes placed in the upper dish container cannot be cleaned as favorably as those in the lower dish container when rice, oil, egg or the like is on the dishes. Thus, there is a limitation to dish container-accommodating direction.